Approximately, by how much does the braking distance increase if speed is doubled?

The braking distance increases approximately with the square of the speed. This means that doubling the speed (e.g., from 50 km/h to 100 km/h) results in a fourfold increase in the braking distance. The tyre marks visible in the photo are the result of hard braking, and their length depends on the initial speed. That's why it is so important to adjust your speed to the conditions, as even a small increase drastically extends the distance needed to stop the vehicle.